1. Field of the Invention
The present invention relates to a pressure sensor, and more particularly, to a pressure sensor for sensing a comparatively high pressure, e.g., 50 kg/mm.sup.2 or more, of a hydraulic pressure or combustion pressure of an internal combustion engine.
2. Description of the Related Art
In the prior art, pressure sensors using a piezoceramic material, metal strain gauge or semiconductor strain gauge are generally known. Among these pressure sensors, where a piezoceramic material is used, there is a difficulty when measuring a pressure in maintaining a pressurized state, since the pressure changes are measured by acceleration, and even if pressure can be measured, signal processing becomes complex. Further, pressure sensor using the metal strain gauge does not have a good sensitivity. On the other hand, a pressure sensor using the semiconductor strain gauge has a good sensitivity and a value of the pressure is output in proportion thereto. Thus, signal processing can be easily carried out. However, the semiconductor type pressure sensors which commercially available are used for measuring only low pressures, and a semiconductor type sensor for measuring high pressures of a combustion pressure of the internal combustion engine, e.g., 50 kg/cm.sup.2 or more is not available on the market. In a conventional semiconductor type sensor, a semiconductor substate acts as a pressure bearing portion, and the ability thereof to withstand pressure is low.
Japanese Examined Patent Publication (Kokoku) No. 58-5372 discloses a pressure sensor wherein a strain gauge is provided on a metal diaphragm. The strain gauge disclosed in this publication is directly adhered to a diaphragm by vapor deposition and bonding, and thus the strain gauge would appear to be a metal strain gauge; since a semiconductor strain gauge cannot be bonded to metal by the above mentioned process.
Japanese Unexamined Patent Publication (Kokai) No. 57-48629 discloses a pressure sensor using piezoceramic material. In the pressure sensor disclosed in the above mentioned publications Nos. 58-5372 and 57-48629, a high sensitivity linear output cannot be obtained at a high pressure.